Of course if you can bring a lot of traffic, referral is a no-brainer but i don't think that it is considered gambling more than in the sense you don't know how many results you will get and when.
Agreed. I probably shouldn't have allowed referral/affiliate work into the final list.. it is *not* gambling/betting as you say. It is business.
I guess it depends how you look at it. The time you spend is valuable and it is a gamble that your time will be worthwhile or not. Not everything should be looked at in terms of money.